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Abstract

Broad relationships among bacteria can be identified by ribosomal RNA analysis, but the
resulting groups may not be easily definable by phenotypic characteristics. This is exemplified by
the genus Campylobacter, which consists of at least three separate groups that cannot be
differentiated readily by phenotypic characteristics.

Examination of the type strains of all Campylobacter species (except Campylobacter pylori),
Wolinella recta, Wolinella curva, Bacteroides ureolyticus, and Bacteroides gracilis revealed that
sheathed flagella occur only in species of rRNA group II (except W.succinogenes). This is helpful in
differentiating this group.

Campylobacters are microaerophilic: they can respire with oxygen but cannot grow at the
full level of oxygen found in an air atmosphere (21% 02). Although W. recta, W. curva, B.
ureolyticus, and B. gracilis are closely related to the campylobacters of rRNA group I, they were
thought to be anaerobes, incapable of oxygen-dependent growth and of respiring with 02. However,
the present study revealed that they are in fact microaerophiles. They exhibited oxygen-dependent
growth but failed to grow at 21% 02 and grew only very slightly under anaerobic conditions unless
provided with electron acceptors such as fumarate and nitrate. They exhibited 02 uptake with H2 or
formate as electron donors (W. recta showed only a low 02 uptake with H2). Oxygen uptake was
inhibited by KCN and 2-heptyl-4-hydroxyquinoline N-oxide. The organisms possessed membrane
bound cytochromes (cytochromes b560 and C551-553, and a CO-binding cytochrome c), as well as
soluble cytochrome C552 and CO-binding cytochrome c. The cytochromes were reduced by H2 and
formate as electron donors. Proton efflux from cells in anaerobic suspensions containing H2 or
formate occurred upon addition of a pulse of oxygen. With formate as the electron donor, H+/O
ratios of W. curva, W. recta, B. ureolyticus, and B. gracilis were 0.75, 1.66,2.06, and 2.04, respectively.
With H2 as the electron donor, H+/O ratios of W.curva, B. ureoyticus, and B. gracilis were 1.25,
1.97, and 2.36, respectively; technical difficulties prevented measurement of the ratio in W. recta.
Proton translocation was inhibited by the protonophore carbonylcyanide m-chlorophenylhydrazone.
The results confirm the relationship of these organisms to campylobacters.